Electrolytic mercury coulometer including a slotted tube for containing mercury



Aug. 26, 1969 L. CORRSIN 3,464,009 ELECTROLYTIC MERCURY COULOMETER INCLUDING A SLOTTED TUBE FOR CONTAINING MERCURY Filed Oct. 22, 1965 FIG. 8

I N VENTOR. LESTER CORRSIN BY I ATTORNEY United States Patent ELECTROLYTIC MERCURY COULOMETER IN- CLUDING A SLO'ITED TUBE FOR CON- TAININ G MERCURY Lester Corrsin, Penfield, N.Y. (18 Wurts Ave., New Paltz, N.Y. 12561) Filed Oct. 22, 1965, Ser. No. 502,065 Int. Cl. G01r 27/22 US. Cl. 324-93 4 Claims ABSTRACT OF THE DISCLOSURE An electrolytic mercury coulometer in which a column of mercury is confined by reason of its surface tension in a longitudinally slotted capillary. An electrolyte extends through the slot to contact the mercury for electrolysis.

This invention relates to a novel electrolytic coulometer, and more particularly to a novel coulometer of this type which is of compact construction and capable of operating at relatively high currents.

Mercury coulometers, which measure the flow of electric current by the electrolytic transfer of mercury between a pair of mercury electrodes, have been found useful for many different purposes, both as current integrators and as operating time indicators. They have, however, been limited heretofore by the need to restrict current flow in them so as to avoid gassing at the electrodes. In the device, for example, shown by Beusman in Patent No. 3,193,763, ions dissolved at the anode must diffuse laterally through a porous medium, typically filter paper, to reach the cathode.. The electrolyte at the cathode becomes depleted of mercury ions if an attempt is made to pass more than a very small current, and hydrogen is then deposited at the cathode, substantially destroying the effectiveness of the coulometer. The permissible current density is limited by the relatively slow transfer of mercury ions between the electrodes.

In the coulometers of the present invention, this problem is substantially overcome and much higher currents may be passed than heretofore, so that the coulometers of the invention are suitable for many utilizations where coulometers of this general type could not be satisfactorily used heretofore such as, for example, for measuring relatively short time intervals.

The invention will now be described in greater detail in connection with the accompanying drawing, wherein;

FIGURE 1 is a plan view of a coulometer according to a first embodiment of the invention;

FIGURE 2 is a cross-sectional view taken along the line 2-2 of FIGURE 1;

FIGURE 3 is a cross-sectional view taken along the line 33 of FIGURE 1;

FIGURE 4 is a cross-sectional view taken along the line 44 of FIGURE 1;

FIGURE 5 is a cross-sectional view, generally similar to the view of FIGURE 2, but illustrating a modified form of the invention;

FIGURE 6 is a cross-sectional view, generally similar to the view of FIGURE 2, but illustrating another modification of the invention;

FIGURE 7 is a cross-sectional view, generally similar to the view of FIGURE 2, but showing still another modification of the invention;

FIGURE 8 is an elevational view, partly in section, and with parts broken away, showing a coulometer according to yet another form of the invention, wherein a mercury column is confined within a slotted tube;

FIGURE 9 is a cross-sectional view taken along the line 99 of FIGURE 8; and,

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FIGURE 10 is a cross-sectional view generally similar to the view of FIGURE 9, but illustrating still another form of the invention in which the mercury column is enclosed within a porous tube.

Briefly, the invention in most of its principal embodiments contemplates an electrolytic coulometer wherein the electrolyte is confined by surface tension between two bodies of mercury, and is not retained in a separate porous matrix, but constitutes a substantially homogeneous liquid body extending between the two bodies of mercury. The arrangement permits the use of a relatively high current density in the electrolysis, because the ion transfer between the two mercury electrodes is not dependent solely upon diffusion and the electric field, but is greatly accelerated by the stirring action produced at the interfaces between the electrolyte and the mercury. Agitation of the mercury surface due to electrolysis is described in a report in Chemical and Engineering News for Sept. 16, 1963, at page 60. This practice of the invention takes advantage of this agitation, by reason of the heretofore unappreciated stirring of the electrolyte caused by it.

In a modified form of the invention, the mercury comprising one electrode of the coulometer is confined in a porous tube immersed in an electrolyte adjacent to a counter electrode of relatively large area. This form also permits the use of relatively high current densities, because the ion transfer is through the thickness of the tube Wall, not laterally along it and the counter electrode is of relatively large area.

The practice of the invention in its principal forms relies upon the high surface tension of mercury, which enables it to be confined within a vessel adjacent to a relatively narrow opening in the wall of the vessel without escaping through the narrow opening. In the practice of the invention, the narrow opening permits the entry of the electrolyte to the vessel so that it comes into liquidliquid contact with a portion of mercury therein.

In one of its forms, the coulometer of the invention may consist of a body having two elongated, juxtaposed capillary bores in it, preferably connected at one end in a U-shaped configuration, and a slot extending laterally between the bores part way along them, and opening laterally into both of them. Mercury is contained in the bores, and electrolyte in the slot. Separate electrical connections are made to the mercury in the respective bores, and a direct current is passed between them, causing mercury to the dissolved from one bore and deposited in the other. The full length of the slot constitutes the contact zone between the mercury and the electrolyte, and agitation of the mercury by the electrolysis produces stirring of the electrolyte so that relatively high current densities can be used. Preferably, the portions of the bores that are not filled with mercury are filled with a waterimmiscible liquid so that in the event the mercury column in either bore is permitted to become shorter than the slot, the electrolyte will not escape from the slot and enter the bore, but will remain confined.

In a modified form of the invention, the mercury is confined within a slotted tube immersed in an electrolyte adjacent to a counter electrode, which may be, for example, a film of mercury supported upon a platinum surface. Because of its relatively high surface tension, the mercury within the tube doesnot escape through the slot. The surface tension of the electrolyte, however, is relatively low so that it does penetrate through the slot and come into contact with the mercury. Alternatively, according to this embodiment of the invention, the slotted tube may be replaced by a porous one, such as, for example, one made of leached or etched glass or the like.

Referring now to the drawing, FIGURE 1 to 4 illustrates a coulometer according to a first embodiment of the invention. The coulometer includes a laminated body 10 of a preferably transparent, insulating material such as glass or a transparent plastic, having two elongated capillary bores 16 and 18 in juxtaposed position and connected together at one end by a bight portion 20 to form a single, generally U-shaped passageway not separately designated). The ends of the bores 16 and 18 opposite from the bight portion 20 are closed by any convenient means such as, for example, by the plug 21 shown, which may be of wax or a synthetic resin.

The body with the bores 16 and 18 and the bight portion 20 may be made by any desired means such as by laminating two plates 12 and 14 that have been appropriately grooved, as by cutting or by chemical etching, or it may be made by the method taught by Beusman in the hereinabove identified patent, according to which one or both of the plates are deformable under heat and pressure, and the plates are laminated under heat and pressure with a wire between them. The wire is later withdrawn, leaving the defined opening between the plates.

In the coulometer of the invention, a slot 22 extends laterally between the bores 16 and 18. In instances where variations of internal resistance during operation of the coulometer are of little consequence, the slot 22 may extend the full length of the bores and open into the bight portion 20. In cases where it is desired that the coulometer have a relatively constant internal resistance, as in most utilizations, the slot 22 is of limited length, and extends from the closed ends of the bores only part way along them.

The bores 16 and 18 are partly filled with mercury columns 26 and 28, respectively, and the slot 22 is filled with an eletrolyte 30, which may be, for example, an aqueous solution of 0.5 normal mercuric iodide and 7.0 normal potassium iodide. The mercury columns 26 and 28 extend to the closed ends of the bores 16 and 18, and in operation are preferably always kept longer than the slot 22, so that throughout its operating range, the internal resistance of the coulometer remains constant.

The ends of the mercury columns 26 and 28 facing the bight 20 are separated by a slug of insulating material, which may be air, but is preferably a water-immiscible liquid such as mineral oil as hereinabove explained.

Electrode connections 32 and 34 are sealed through the body 10 into the bores 16 and 18 at the respective closed ends thereof to contact the mercury columns 26 and 28 for connecting them to an external circuit. As shown, an auxiliary electrode 36 is sealed through the body 10 into the bight 20 for producing an electrical output signal in response to the elongation or shortening of the one mercury column 28. Illustratively, the signal may be produced by closing of an auxiliary circuit to energize a relay 88 at such time as the electrolysis has proceeded to the point where suflicient mercury has been transferred into the bore 18 to cause the mercury column 28 therein to come into contact with the auxiliary electrode 36.

The embodiment shown in FIGURE is substantially similar to the embodiment shown in FIGURES 1 to 4, except that the bores 16 and 18' are formed by grooves cut only in one plate 12 of the laminated body and a substantially fiat, transparent cover plate 40 replaces the grooved plate 14.

In a third form of the invention, as shown in FIGURE 6, the coulometer is generally similar to the coulometer shown in FIGURES 1 to 4, but is made of two generally similar plates 12" and 14" arranged in confronting relationship, each of the plates 12" and 14" having a relatively deep groove 42 with a flat bottomed, relatively shallow shoulder 44 extending laterally from it to form the slot 22 (not designated in FIGURE 6). The two plates 12" and 14" are laminated in opposed registration. The grooves 42 form the capillary bores 16 and 18 and the shoulders 44 register to form the slot 22 (not designated in FIGURE 6).

Another coulometer according to the invention as shown in FIGURE 7, is generally similar to the coulom- 4 eter shown in FIGURES 1 to 4, but is made of two flat plates 40' and 41" laminated with shims 46 and 48 between them to define the capillary bores 35 and 37. The central, longitudinally, extending shim 48 is thinner than the two outer shims 46 over a portion of its length to define the slot 22, and is sufliciently shorter than the outer shims 46 to leave space to define the bight portion between the two grooves, or bores, so that, in plan, the arrangement is generally similar to that shown in FIGURE 1.

To facilitate loading of the liquids into the coulometer during manufacture, holes 47 and 49 are formed through the thickness of one of the plates 12 and 14 leading, respectively, into the bight portion 20 and into the slot 22. The liquids may all be inserted by hypodermic needle, after which the holes 47 and 49 are plugged. Preferably, the mercury is inserted first, filling both bores 16 and 18 and the bight portion 20. The ends of the bores 16 and 18 and of the slot 22 opposite from the bight portion 20 are initially open. After the mercury is inserted, the desired quantity of oil is injected through the hole 47, after which electrolyte is injected through the second hole 49 to fill the slot. The open ends of the bores and the slot are then closed and sealed by a plug 21.

To facilitate insertion of the electrolyte, and to ensure against the entrapment of air in the slot 22, it is preferred to treat the surfaces of the slot with a wetting agent such as a silica sol, which may be painted on the surfaces and allowed to dry before assembly. The electrolyte then fills the slot 22 by capillary attraction and drives out the air substantially completely.

Two alternative further modifications of the invention are shown in FIGURES 8 and 10. The embodiment shown in FIGURES 8 and 9 includes a slotted capillary tube 50, which is preferably transparent and of about 1 mm. to 2 mm. inside diameter. It is mounted vertically within an envelope 54 filled with an electrolyte 56. A counter electrode 58 is mounted within the envelope 54 confronting the slot 52 of the tube. The counter electrode may be, for example, a body of mercury confined behind a porous diaphragm, or, alternatively, a platinum film adherently coated on a plate of glass or other material insoluble in the electrolyte and wetted with mercury. Mercury wets platinum and adheres strongly to it, so that it covers the entire platinum surface, and because of capillary 0 action and its own surface tension, it tends to fill up any small grooves or indentations in the platinum surface. The platinum surface is preferably striated, or dimpled, so that it will hold a quantity of mercury adequate to fill the tube 50 from about the top of the counter electrode 58 to the maximum operating range of the coulometer. By making the counter electrode 58 relatively short, and restricting the operation of the device so that the column of mercury 55 within the slotted tube 50 never becomes shorter than the counter electrode 58, the internal resistance of the coulometer is maintained at a relatively constant value throughout its operating range.

According to an alternative design, as shown in FIG- URE 10, the slotted tube 50 may be replaced by a porous tube 50' such as one of leached glass or a perforated plastic.

What is claimed is:

1. An electrolytic coulometer comprising a body of an insulating material having two juxtaposed capillary bores therein and a slot extending between said bores and opening laterally into them, said slot being thinner than said bores, a liquid metal in said bores, an electrolyte substantially filling said slot and in liquid-liquid contact with said metal in said bores, said bores and said slot being completely enclosed within said body, and electrodes sealed through the material of said body into said bores for electrically connecting the metal therein to an external source of electricity, the metal being constrained by its own surface tension from escaping into said slot.

2. An electrolytic mercury coulometer comprising a body of an insulating material having two juxtaposed capillary bores therein joined at one end by a bight passageway and sealed at the other end, said body having a slot extending between said bores and opening laterally into them, said slot being thinner than said bores and extending from the sealed ends thereof only part way along them, mercury in said bores extending in the form of columns from the sealed ends thereof part way toward said bight passageway, an electrolyte completely filling said slot and in liquid-liquid contact with the mercury in said bores, said electrodes sealed through the material of said body into said bores for connecting the'rnercury therein to an external source of electricity, the mercury being constrained by its own surface tension from escaping into said slot.

3. An electrolytic mercury coulometer comprising a laminatd body composed of an arrangement of shims sealed between two flat plates to form a unitary body having two juxtaposed capillary bores therein joined at one end by a bight passageway and sealed at the other end, and having a slot extending between said bores and opening laterally into them, said slot being thinner than said bores and extending from the sealed ends thereof only part Way along them, mercury in said bores extending in the form of columns from the sealed ends thereof part way toward said bight passageway, an electrolyte completely filling said slot and in liquid-liquid contact with the mercury in said bores, and electrode means for connecting the mercury in said bores to an external source of electricity, the mercury being constrained by its own surface tension from escaping into said slot.

4. An electrolytic mercury coulometer comprising an elongated vessel, a capillary tube within said vessel and extending approximately the full length thereof, said tube having a longitudinal slot in its wall, a counter electrode in said vessel adjacent to said tube, confronting said slot, and extending along a predetermined length of said tube at one end thereof, said one end being the bottom of said tube when the coulometer is supported in vertical position for normal operation, a mercuric electrolyte in said vessel in a quantity to cover said predetermined length of said tube when the coulometer is in its normal operating position, mercury in said tube, said mercury being constrained by its own surface tension from escaping through said slot, said counter electrode including mercury and all other parts thereof being insoluble in said electrolyte, and means for connecting the mercury in said tube and said counter electrode to an external electrical circuit.

References Cited UNITED STATES PATENTS 1,557,931 10/ 1925 Grossmann 32494 3,343,083 9/1967 Beusman 32494 3,045,178 7/1962 Corrsin 32494 XR FOREIGN PATENTS 893,532 7/1949 Germany. 324,271 9/1917 Germany.

9,746 5/1900 Great Britain.

RUDOLPH V. ROIJINEC, Primary Examiner E. F. KARLSEN, Assistant Examiner U.S. Cl. X.R. 324-68, 94 

